Tanks for the storage of liquids are well known and have been constructed for many years. These tanks can be constructed in a variety of ways and from a variety of materials. Often liquids are stored in underground tanks. For this and other reasons relating to leak prevention, fittings through which liquid is introduced or removed are often at the top of the tank.
When hazardous or valuable liquids are stored it becomes desirable to prevent these liquids from escaping due to leaks in the fittings or the pump outside and/or above the tank. In addition, it is desirable to prevent leaks that may occur at other points, such as connections between the fittings and other piping, and that may also occur at the juncture where fittings pass through tank walls. Additionally, it is desirable to prevent rain water and other liquids as well as solids from mixing in with the liquid being stored.
For safety reasons liquid storage tanks, particularly when designed for underground use, are now preferably constructed with a double wall. A convenient method of building a double wall tank is disclosed in U.S. Pat. No. 4,640,435 and subsequent patents relating thereto.